Gravitationally Unstable Hydrous Melts at the Base of the Upper Mantle

IF 3.9 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Journal of Geophysical Research: Solid Earth Pub Date : 2025-04-23 DOI:10.1029/2024JB030737

Hongzhan Fei, Juan Chen, Fei Wang, Baohua Zhang, Qunke Xia, Tomoo Katsura

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Abstract

The water-rich mantle transition zone in contrast to the low water storage capacity of the upper mantle suggests the presence of hydrous melts near the 410-km discontinuity. However, the gravitational stability of the melts is under debate. Since melt density is strongly correlated to its H₂O content, we systematically determined the pressure, temperature, and compositional dependences of H₂O contents in hydrous melts by high-pressure experiments combined with mass balance calculations. Subsequently, we estimated the density of hydrous melts at 410-km depth based on the H₂O content and equation of state of H₂O at high pressure. The hydrous melts are found to be buoyant near the 410-km discontinuity. Therefore, as far as melts are formed, they may migrate upward, resulting in the water circulation maintained by slab subduction. The upwelling melts may hydrate the upper mantle minerals continuously, leading to a low seismic velocity, high electrical conductivity, and water-saturated deep upper mantle.

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重力不稳定的水在上地幔底部融化

富水的地幔过渡带与上地幔低储水能力的对比表明，在410公里的不连续面附近存在含水熔体。然而，熔体的重力稳定性仍存在争议。由于熔体密度与其H2O含量密切相关，我们通过高压实验结合质量平衡计算系统地确定了含水熔体中H2O含量的压力、温度和成分依赖性。随后，我们根据水的含量和高压下水的状态方程估算了410 km深度含水熔体的密度。发现含水熔体在410公里的不连续面附近具有浮力。因此，只要熔体形成，它们就可能向上迁移，造成由板块俯冲维持的水循环。上涌的熔融体可能会不断地对上地幔矿物进行水化作用，从而导致低地震速度、高电导率和上地幔深部水饱和。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Journal of Geophysical Research: Solid Earth Earth and Planetary Sciences-Geophysics

CiteScore

7.50

自引率

15.40%

发文量

559

期刊介绍： The Journal of Geophysical Research: Solid Earth serves as the premier publication for the breadth of solid Earth geophysics including (in alphabetical order): electromagnetic methods; exploration geophysics; geodesy and gravity; geodynamics, rheology, and plate kinematics; geomagnetism and paleomagnetism; hydrogeophysics; Instruments, techniques, and models; solid Earth interactions with the cryosphere, atmosphere, oceans, and climate; marine geology and geophysics; natural and anthropogenic hazards; near surface geophysics; petrology, geochemistry, and mineralogy; planet Earth physics and chemistry; rock mechanics and deformation; seismology; tectonophysics; and volcanology. JGR: Solid Earth has long distinguished itself as the venue for publication of Research Articles backed solidly by data and as well as presenting theoretical and numerical developments with broad applications. Research Articles published in JGR: Solid Earth have had long-term impacts in their fields. JGR: Solid Earth provides a venue for special issues and special themes based on conferences, workshops, and community initiatives. JGR: Solid Earth also publishes Commentaries on research and emerging trends in the field; these are commissioned by the editors, and suggestion are welcome.